Numerous means have been sought to improve the fuel-efficiency of moving bodies, and especially moving bluff bodies, by reducing their aerodynamic drag. In the field of surface transportation, and particularly in the long-haul trucking industry, even small improvements in fuel efficiency can reduce annual operating costs significantly. It is therefore advantageous in the design of a vehicle to reduce drag forces, thereby increasing the aerodynamic properties and efficiency of the vehicle.
The over-the-highway cargo hauling tractor-trailer combination is one vehicle that experiences excessive aerodynamic drag. Generally described, tractor-trailer combinations typically include a tractor having a so-called fifth wheel by which a box-like semi-trailer may be articulatedly attached to the tractor for transportation of the semi-trailer. By providing the articulated connection via the fifth wheel, a space or gap is formed between the aft facing rear wall of the tractor cab and the forward facing front wall of the semi-trailer. It is well known that this gap, or the gap between succeeding trailers (not shown) of a tractor trailer combination causes wake regions and, as a result, aerodynamic drag.
Another reason for large pressure drag on tractor-trailer combinations is the configuration of the tractor front section, particularly, the presence of a sharp angle located at a lower edge of the truck bumper and the passage of airflow underneath the vehicle and associated trailer. At highway speeds, such underbody air flow interacts with undercarriage components, such as wheel assemblies, skid plates, oil pans, transmission housings, drive shafts, chassis structure, etc., which in turn, develops a substantial amount of turbulent airflow in the underbody region of the vehicle and/or trailer.